I'M trying to install Limewire on Ubuntu Linux but I'M getting the following error message.

Failed to run gdebi-gtk '--non-interactive' '/home/other/Desktop/LimeWireLinux.deb' as user root.

The underlying authorization mechanism (sudo) does not allow you to run this program. Contact the system administrator.

I am also not able to login into the Terminal using the "su" command to install other programs. I the this error message, even though I'M using the same password I use to login to the screen name.

su: Authentication failure
other@garrett-desktop:~$
other@garrett-desktop

Thanks for any and all help.